fix: add bound check for Yc_length against server DH params#5737
Merged
CarolYeh910 merged 6 commits intoaws:mainfrom Feb 18, 2026
Merged
fix: add bound check for Yc_length against server DH params#5737CarolYeh910 merged 6 commits intoaws:mainfrom
CarolYeh910 merged 6 commits intoaws:mainfrom
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maddeleine
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Feb 17, 2026
maddeleine
reviewed
Feb 17, 2026
jouho
reviewed
Feb 17, 2026
jouho
approved these changes
Feb 18, 2026
maddeleine
approved these changes
Feb 18, 2026
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Goal
Bound the length of
Yc_inbuffer against the size of server DH parametersWhy
s2n_dh_compute_shared_secret_as_server()reads a peer-suppliedYc_inbuffer without validating its length against the server DH group size. This allows clients to send oversizedYc_lengthvalues (up to 65535 bytes) and cause unnecessary memory allocation and CPU workload.How
Validate
Yc_lengthdoes not exceedserver_dh_params_sizebefore invokingBN_bin2bn()orDH_compute_key().Callouts
We would like to thank Joshua Rogers (https://joshua.hu/) of AISLE Research Team (https://aisle.com/) for reporting this issue.
Testing
I added a unit test to verify that s2n server will fail for
S2N_ERR_DH_SHARED_SECRETwhen a client sends an oversizedYc_inbuffer. One thing to note is that the selected parameters in this test may causes2n_pkcs3_to_dh_params()to fail on certain libcryptos due to different behaviors ofDH_check()across versions. The purpose is not testingDH_check(), thus skipping the test whens2n_pkcs3_to_dh_params()fails.By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.